1. Field of the Invention
The present invention relates to a camera apparatus including an optical system, and more particularly, to a camera apparatus including an optical element which is insertable to and removable from an optical path of the optical system, and an image pickup apparatus including the same.
2. Description of the Related Art
Conventionally, there is known an image pickup apparatus that suppresses a variation of an image forming position due to insertion and removal of an optical element in an optical path by giving refractive power to the optical element to be inserted in the optical path.
For instance, Japanese Patent Application Laid-Open No. S63-025612 discloses an invention of giving refractive power to an optical element to be inserted in order to correct a change of an image forming position when the optical element is inserted. When a flat plate optical element is inserted between an image pickup lens and an image forming surface, or in a lens system of the image pickup lens, the image forming position is shifted to the over side (namely, the opposite side to the object side). In Japanese Patent Application Laid-Open No. S63-025612, positive refractive power is given to the optical element to be inserted so that the movement of the image forming position is canceled.
However, in the conventional technology described in Japanese Patent Application Laid-Open No. S63-025612, insertion and removal of the optical element causes a change in optical characteristic. For instance, if refractive power is given to the optical element to be inserted so as to cancel the shift of the image forming position as described in Japanese Patent Application Laid-Open No. S63-025612, an under-corrected spherical aberration occurs when the optical element is inserted. FIG. 9 illustrates a schematic diagram of the spherical aberration when the shift of the image forming position is canceled as described in Japanese Patent Application Laid-Open No. S63-025612. In FIG. 9, a dashed dotted line 902 indicates aberration when the optical element is not inserted in the optical path, a broken line 901 indicates aberration when the optical element is inserted in the optical path, and a position SA205 is an image pickup surface. Because of this spherical aberration, quality of the obtained image is deteriorated. In addition, best focus positions (903 and 904) that can be expressed as a position where a root mean square (RMS) of a spot diameter of an axial light beam in a spot diagram 901 becomes smallest are not within a focal depth (903). Then, an influence of the insertion and removal of the optical element on the image becomes so conspicuous that the obtained image changes largely.